This invention relates to methods of and apparatus for straightening rods and particularly relates to methods and apparatus for straightening tapered mandrels used in the manufacture of non-metallic composite shafts for golf clubs.
Many mechanisms and devices include rods of selected cross sectional configurations which, desirably, have a linear axis from a first end to a second end thereof. The rods could be solid or hollow in tubular fashion. The rods could also be referred to as shafts, tubes, mandrels, pipes, elongated members or the like. In any event, in order for the mechanisms and devices to function properly, the axis of each of the rods must be linear.
In one process for manufacturing golf clubs, a tapered shaft is formed from a non-metallic material such as, for example, graphite and has a club head assembled at a tip end of the shaft and a grip assembled at a butt end of the shaft. A shaft of this type is commonly referred to as a composite shaft. In order for the club to function properly when used by a golfer, the axis of the composite shaft must be straight. Thus, during the process of manufacturing the composite shaft, critical attention must be directed to insuring that the axis of the resultant shaft is linear.
When making a composite shaft, graphite ribbons are wrapped around a solid metal mandrel of a prescribed length. Each of the ribbons also includes a plurality of spaced, parallel, plastic fibers which extend along the length of the ribbon or on a bias to the length of the ribbon. A heat-shrinkable plastic is wrapped around the assembly of the mandrel and the ribbons. The assembly is then processed through a heated environment where the graphite composite becomes liquid and the heat-shrinkable plastic shrinks to a desired size to confine the liquid graphite composite to the desired size. The assembly is then removed from the heated environment and is cooled whereby the graphite cures in the shape defined by the heat shrunk plastic. The plastic and the mandrel are removed and the resultant composite shaft is processed further to finish the shaft for use as a shaft of a golf club.
It is apparent from the foregoing description of the manufacture of the composite shaft that the straightness, or non-straightness, of the axis of the mandrel establishes the resultant straightness, or non-straightness of the axis of the shaft. If the mandrel is not axially linear, the shaft likewise will not be axially linear and will have to be discarded. Thus, it is critically important that the axis of the mandrel be straight when the mandrel is to be used in the manufacture of the composite shaft.
Mandrels which are used in the manufacture of composite shafts for golf clubs are typically solid and are formed with a first or large diameter end and a second or small diameter end with a sidewall which tapers inwardly from the first end to the second end thereof. The tapered sidewall is circular or round and the axis is desirably straight or linear. The large diameter of the mandrel could be, for example, 0.5 inch and the small diameter could be, for example, 0.125 inch while the length could vary within a range from 39 inches to 45 inches. With such small diameters, and with a relatively long length, it is not uncommon for the mandrels to bend slightly during handling and storage. This is particularly so along a length of about eighteen inches as measured from the small diameter end toward the other end. In order to insure that each mandrel is formed with a linear axis during manufacture of the shaft, the mandrel should be processed through a mandrel-straightening apparatus before the graphite ribbons are wrapped onto the mandrel.
A device for straightening tapered elongated elements is disclosed in U.S. Pat. No. 3,998,083 and includes structure for rotating and advancing the element along a longitudinal axis. The element is located within a sheath composed of a coiled spring construction during the straightening operation. During the straightening operation, the sheath with the tapered element assembled therein is processed through an universal mechanism where the tapered element is bent back and forth across its axis. A device of this type is complex and expensive. Further, such a device requires considerable load and unload time thereby limiting the number of elements which can be straightened within a given period of time.
Other straightening devices are shown and described in U.S. Pat. Nos. 3,492,850 and 4,287,743, each of which use rollers which bear against the element to be straightened as the element is moved adjacent the rollers. Still another straightening device is shown and described in U.S. Pat. No. 3,812,700 wherein an element to be straightened is moved through a drum which contains spaced radially-inwardly directed straightening members. As the drum is rotated and the element is pulled through and along the axis of the drum, the members engage the bent, out-of-axis portions of the element and urges the portions toward the drum axis to thereby straighten the element. Each of these devices are also complex and expensive while requiring significant loading and unloading time. Also, due to the individual movement of the element-engaging structure with the elements during the straightening operation, the element could be subject to unwanted stresses during the operation.
In any event, there is a need for an apparatus for straightening rods and the like, such as tapered mandrels for example, in an inexpensive and uncomplicated manner while avoiding placing unnecessary stresses on the rod during the straightening operation. In addition, there is a need for an apparatus for straightening only selected portions of rods where out-of-axis bending is likely to occur rather than randomly along the entire length of the rod.